This invention provides a relatively simple means of providing the appropriate piston phasing for a two piston Stirling engine while eliminating the troublesome side forces on the pistons. It also permits both pistons to be driven by a common crankpin, at the same time retaining the advantageous parallel cylinder arrangement that is preferred for two piston Stirling engines. A method for balancing the reciprocating inertial forces of the engine with a single additional balance shaft is part of the invention, which method may be also useful in balancing other types of Stirling engines.
The single-acting two piston Stirling engine was well known in the last part of the nineteenth century, when it was generally referred to as the "Rider" engine, after its inventor, A. K. Rider. Its operation is amply described in the literature, and is conceptually identical to one power cycle unit of the four cylinder double-acting Stirling engine that is the focus of most present-day research and development. It is clear from the literature that the single-acting two piston engine is itself appropriate for certain power applications, but perhaps as important would be its use as an experimental "part engine" for the continuing development of the double-acting four cylinder engine.
It is widely recognized that side forces on the piston of the conventional crank and slider mechanism give rise to friction and lubrication difficulties when directly applied to simple Stirling engines. For long engine life, all traces of liquid lubricant must be excluded from the engine's power cylinders, and yet unlubricated pistons cannot absorb any appreciable side forces without causing excessive friction and wear. Separate crossheads have been used in some designs to separate the lubricated portion of the engine from the pistons and power cylinders, but on simple single-acting engines this approach unduly increases weight and complexity.
The aim of this invention is to provide a relatively simple crankshaft mechanism for the two piston Stirling engine which will allow the use of unlubricated pistons, without increasing friction or wear, by substantially eliminating side forces on the pistons. At the same time, parallel cylinders are retained, allowing desirably short passageways to connect the cylinders. The crankshaft requires only a single throw, and it may be light-weight and of extremely simple design and manufacture. The reciprocating inertial forces may simply be balanced by the generalized method of balance which is part of this invention.
Other aims, features, and advantages will be apparent in the description, below.